package org.apache.lucene.util;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.util.BitSet;

import org.apache.lucene.search.DocIdSet;
import org.apache.lucene.search.DocIdSetIterator;

/** Simple DocIdSet and DocIdSetIterator backed by a BitSet */
public class DocIdBitSet extends DocIdSet {
    private BitSet bitSet;

    public DocIdBitSet(BitSet bitSet) {
        this.bitSet = bitSet;
    }

    @Override
    public DocIdSetIterator iterator() {
        return new DocIdBitSetIterator(bitSet);
    }

    /** This DocIdSet implementation is cacheable. */
    @Override
    public boolean isCacheable() {
        return true;
    }

    /**
     * Returns the underlying BitSet. 
     */
    public BitSet getBitSet() {
        return this.bitSet;
    }

    private static class DocIdBitSetIterator extends DocIdSetIterator {
        private int docId;
        private BitSet bitSet;

        DocIdBitSetIterator(BitSet bitSet) {
            this.bitSet = bitSet;
            this.docId = -1;
        }

        @Override
        public int docID() {
            return docId;
        }

        @Override
        public int nextDoc() {
            // (docId + 1) on next line requires -1 initial value for docNr:
            int d = bitSet.nextSetBit(docId + 1);
            // -1 returned by BitSet.nextSetBit() when exhausted
            docId = d == -1 ? NO_MORE_DOCS : d;
            return docId;
        }

        @Override
        public int advance(int target) {
            int d = bitSet.nextSetBit(target);
            // -1 returned by BitSet.nextSetBit() when exhausted
            docId = d == -1 ? NO_MORE_DOCS : d;
            return docId;
        }
    }
}
